The image sensor of the camera is responsible for transforming light into electrical signals. When building a camera, there are two possible technologies for the camera's image sensor: CCD or CMOS.
 

CCD (Charged Coupled Device) and CMOS (Complementary Metal Oxide Semiconductor) are the critical components that act as a camera's "digital film." CCD sensors are produced using a technology developed specifically for the camera industry, while CMOS sensors are based on standard technology already extensively used in memory chips--inside PCs, for example. Today's high quality cameras use mostly CCD sensors. Although recent advances in CMOS sensors are closing the gap, they are still not suitable for cameras where the highest possible image quality is required. However, CMOS sensors may be ideal for entry-level network cameras where size and price are important factors.

CCD technology

CCD sensors have been used in cameras for more than 20 years and present many advantageous qualities; among them, better light sensitivity than CMOS sensors. This higher light sensitivity translates into better images in low light conditions. CCD sensors are, however, more expensive as they are made in a non-standard process and more complex to incorporate into a camera. In addition, when there is a very bright object in the scene (such as a lamp or direct sunlight), the CCD may bleed, causing vertical stripes below and above the object. This phenomenon is called a smear.

CMOS technology

Recent advances in CMOS sensors bring them closer to their CCD counterparts in terms of image quality, but CMOS sensors remain unsuitable for cameras where the highest possible image quality is required. CMOS sensors provide a lower total cost for the cameras since they contain all the logics needed to build cameras around them. They make it possible to produce smaller-sized cameras. Large-sized sensors are available, providing megapixel resolution to a variety of network cameras. A current limitation with CMOS sensors is their lower light sensitivity. While this drawback is not an issue in bright environments, in low light conditions it becomes apparent. The result is either a very dark or a very noisy image.